HAR-NDS is a structure found as a third circulating system for meridian systems and meridian points in the 1960s, and also named the “Bonghan System” or “primo vascular system.” The HAR-NDS was known to have a network structure, which is composed of nodes and ducts, and form a network on organ surfaces, inside blood vessels, inside lymphatics, and along skin and nervous system (Kim BH [Non-Patent Document 1]; Soh K S [Non-Patent Document 2]; Lee et al. [Patent Document 1]). It has been also seen that a node of the HAR-NDS is filled with innate immune cells and particularly, mast cells, eosinophils, basophils, neutrophils and monocytes (histiocytes) are rich in the node of the HAR-NDS (Kwon B S et al. [Non-Patent Document 3]).
Stem cells refer to cells that have self-regenerative and proliferative potentials and also have potential for differentiating into various tissue cells and may be classified into totipotent stem cells, pluripotent stem cells and multipotent stem cells.
An appropriate combination of growth factors and cytokines is essential for optimized stem cell culture. Typically, for the optimized stem cell culture, growth factors and cytokines necessary for survival, proliferation and maturation (differentiation) of stem cells, such as a stem cell factor (SCF; Broudy et al. [Non-Patent Document 4]), flt3/flt2 ligand (FL), interleukin (IL), a leukemia inhibitory factor (LIK), thrombopoietin (TPO), and a basic fibroblast growth factor (basic FGF) are used. For example, when the co-culture of hematopoietic stem cells and hematopoietic feeder cells is stimulated by growth factors or cytokines, hematopoietic precursor cells constituting Cobblestone-area forming cells (CAFCs) may be identified. According to this method, existence, proliferation and differentiation of the hematopoietic stem cells may be identified (Nakahata et al. [Non-Patent Document 5], Eaves et al. [Non-Patent Document 6]).
Examples of non-hematopoietic adult stem cells in bone marrow include very small embryonic-like stem cells (VSELs), multipotent adult stem cells, multipotent adult progenitor cells, marrow-isolated adult multilineage inducible cells, mesenchymal stem cells, and endothelial progenitor cells (Zuba-Surma E K et al. [Non-Patent Document 7]; Beltrami A P et al. [Non-Patent Document 8]; Jiang Y et al. [Non-Patent Document 9], Pittenger S C et al. [Non-Patent Document 10]).
Particularly, the VSELs are small-sized embryonic-like stem cells, which rarely populate inside the bone marrow of rodents and humans, negative for lineage and CD45, and are able to express stem cell markers, and differentiate into three germ layers such as ectoderm, mesoderm, and endoderm in vitro (Kucia M et al [Non-Patent Document 11]).
Advanced research on neuronal stem cells has dealt with the hematopoietic stem cells and the bone marrow-derived VSELs and also with the association between the VSELs and the hematopoietic stem cells (Scheffler B et al. [Non-Patent Document 12]; A V, T et al. [Non-Patent Document 13]). Particularly, genes related to the development of neuronal cells (Notch, Delta, neurogenin, OCT, Presenilin, etc.) and growth factors (an epidermal growth factor, NGF, and a brain-derived neurotrophic factor) have been known, and when such growth factors are injected, differentiation of non-hematopoietic adult stem cells having a potential to differentiate into neurons, astrocytes and oligodendrocytes may be observed, and neural differentiation may be identified using neuronal cell markers (GFAP, NeuN, βIII-tubulin, neurofilament, Brn3a, Thy-1, GFAP, vimentin, nestin, and glutamine synthetase). Such a series of procedures is called neuropoiesis or neurogenesis.
The best-known sites where the neuropoiesis of neuronal cells occur are the subventricular zone (SVZ), which is a thin cell layer beneath the surface of the lateral ventricles of the brain, and the subgranular zone (SGZ), which is the dentate gyrus (DG) and the cornu ammonis (CA) in the hippocampus. In the SVZ, neural progenitor cells (type C cells) or neuroblasts (type A neuroblasts) are generated by a reaction between type B1 cells and neural stem cells, migrate to the olfactory bulb through the rostral migratory stream (RMS), followed by maturation into interneurons. In the DG of the SGZ, radial type 1 cells and type 2 cells differentiate into type 3 neuroblasts, migrate to the granule cell layer via immature neurons, then maturate into granule neurons. Also, maturation of pyramidal neurons takes place in the CA region (Goldman et al. [Non-Patent Document 14]; Scheffler, B et al. [Non-Patent Document 15]). Transplantation of such adult stem cells having a potential for differentiation into or regeneration (proliferation) of adult neuronal cells is useful for treating neurodegenerative diseases, peripheral neuropathy, or Parkinson's disease.
Bone marrow-derived adult stem cells or hematopoietic stem cells were identified as described above, and in vitro preparation and differentiation methods for these stem cells had been suggested, but still, there is a basic limit to supplying adult stem cells and hematopoietic stem cells.
Therefore, the inventors attempted to develop new sources of adult stem cells and hematopoietic stem cells and identified that the adult stem cells and the hematopoietic stem cells can be separated from HAR-NDS, and the separated cells can be in vitro proliferated. They also identified that the adult stem cells have an excellent potential for differentiation into neuronal cells and the hematopoietic stem cells have an excellent potential for differentiation into hematopoietic cells, thus, completing the present invention.